We have been studying the in vitro differentiation of human peripheral blood B lymphocytes (B cells) into immunoglobulin (Ig)-secreting cells. Using a microculture method and sensitive reverse plaque assay, we have carefully analyzed the functional role of B and T cells and monocytes involved. When lymphocytes are cultured with pokeweed mitogen (PWM), a subpopulation of T cells is stimulated to proliferate in response to PWM presented by monocytes in association with HLA-DR antigen. These activated T cells secrete soluble factors which help proliferation and maturation of B cells into Ig-secreting cells. The objective of this proposal is to biochemically purify and functionally characterize B-cell growth factors (BCGF) in man. Recently, rapid progress has been made in characterizing T-cell growth factor (interleukin 2) biochemically and functionally. However, progress in BCGF research has been hampered due to the lack of a reliable assay and of sufficiently large quantities of purified BCGF. Hence, we plan to attack this problem by (1) developing a quantitative assay system for BCGF using an activated B-cell line which depends upon the exogenous BCGF for their proliferation; (2) functionally characterizing BCGF in polyclonal B-cell proliferation and differentiation; (3) establishing cloned T cells that produce BCGF; (4) biochemically purifying BCGF to molecular homogeneity; and (5) preparing monoclonal antibody directed to BCGF. The availability of purified BCGF will allow detailed studies on the mechanism of action on activated B blasts. Eventually, purified BCGF will have tremendous potential as a therapeutic reagent. This potential, for example, should first be explored in the in vitro experimental model using periopheral blood lymphocytes of patients with common varied form of hypogammaglobulinemia and then applied to clincal situations where terminal differentiation of activated B blasts is blocked.